焊后热处理对镁合金搅拌摩擦焊接接头的影响

对AZ31B镁合金进行搅拌摩擦焊接,研究热处理前后焊接接头组织及性能的变化。结果表明:焊后热处理可以显著改善焊接接头的力学性能;当搅拌头的旋转速度为600r.min-1,焊接速度为47.5mm.min-1,接头的抗拉强度为168MPa,延伸率为3.6%。热处理后,接头的抗拉强度和延伸率最高可达205MPa和8.6%,比热处理前分别提高22.02%和138.89%;接头的最佳热处理工艺为:退火温度250℃,保温1h;随着退火温度的升高,焊核区晶粒的长大速度大于热影响区/热机影响区混合区域(HAZ/TMAZ)。当退火温度高于250℃时,焊接接头的拉伸断口主要为扁条状韧窝,呈现出微孔聚合韧性断裂特征。

Influences of Post-weld Heat Treatments on Friction Stir-welded AZ31B Magnesium Alloy Joints

Friction stir welding was conducted on AZ31B magnesium alloy. Variation of microstructures and properties of the welding joints before and after heat treatments was studied. The results show that post-weld heat treatments can markedly improve the mechanical properties of the friction stir-welded AZ31B magnesium alloy joints; when the rotating speed of stirring pin is 600 r·min-1 and the welding speed is 47.5 mm·min-1, the ultimate tensile strength can reach 168 MPa and the elongation is 3.6%. After heat treatments, the highest ultimate tensile strength can reach 205 MPa, which is 22.02% higher than that before heat treatments and the elongation is 8.6%, which is 138.89% higher than before heat treatments. The ideal heat treatment technique of the joint is keeping the annealing temperature at 250 oC for 1 h. As the annealing temperature increases, the growing speed of welding nugget zone grain is higher than the heat affected zone/thermo-mechanically affected zone. When the annealing temperature is higher than 250 oC, the morphologies of tensile fracture of welding joints mainly exhibit oblate dimples with a typical ductile dimple-fracture.